FEM: unit tests, add FEM_VTK check and reactivate vtk mesh test
FEM: unit tests, add FEM_VTK check and reactivate vtk mesh test

Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master